Effect of citric acid on the synthesis of ZnWO4/ZnO nanorods for photoelectrochemical water splitting

ZnO nanorods (NRs) and ZnWO4/ZnO heterostructure, using TiO2 seed layers, were synthesized by two steps hydrothermal method and annealed at 450 °C for 2 hr. The results showed that the ZnWO4 was grown on the hexagonal ZnO NRs and change to hierarchically structure when the citric acid content was increased. All samples were applied as photoanode for photoelectrochemical (PEC) water splitting cell. As the result, the 50ZnW/ZnO sample showed the best performance of the PEC water splitting process than others. From the Electrochemical Impedance Spectroscopy (EIS) study, the Nyquist plot of 25ZnW/ZnO and 50ZnW/ZnO samples showed smaller arc compared to ZnO NRs. This is signified that the ZnWO4/ZnO heterostructure has greater charge transfer between the photoanode and electrolyte than the pristine ZnO. Hence, the modified ZnWO4 on the ZnO surface enhances the performance of ZnO NRs based PEC water splitting cell for the UV light hydrogen fuel generation.